I think the hardest bit is actually deciding to stop mate, once you've properly made that decision it is quite straight forward.
But like Peckham says, you need to actually 'want to', not just think you ought to. Just like smoking really, if you just feel you ought to stop you will probably fail because you'll actually still want to smoke, but if you want to stop you'll enjoy the freedom of not smoking.
One other thing that I found with quitting the grog; don't expect to feel much different for about 4 weeks because, apart from not having any hangovers, you probably won't. But after 3 or 4 weeks I started to feel completely different, and it just got better and better, to the point that after 2 or 3 months I literally lost the desire to have a drink completely, as I felt so much better and happier without the stuff.
I'm pretty convinced that a lot of people stop drinking but only for 3 or 4 weeks, and never really feel any benefit of stopping so they go back to it. Whereas if they stopped for over a month they would begin to feel so much better they would probably stay off it. That's what I found anyway.